System for adjusting ventricular refractory periods

ABSTRACT

A system is provided for controlling a left univentricular (LUV) pacing therapy using an implantable medical device (IMD). The system also includes one or more processors configured to determine an atrial-ventricular (AV) conduction interval (ARRV) between the A site and a first RV sensed event at the RV site, determine an inter-ventricular (VV) conduction interval (RLV-RRV) between a paced event at the LV site and a second RV sensed event at the RV site, and set a ventricular refractory period (VRP) based on at least one of the AV conduction interval or the VV conduction interval and a predetermined offset. The one or more processors are also configured to blank signals over the RV sensing channel during the VRP.

BACKGROUND

Embodiments herein generally relate to a system and method for adjustingventricular refractory periods during left ventricle only pacing.

Most conventional pacing algorithms call for pacing in the rightventricle (RV) alone or in combination with left ventricular (LV)pacing. However, certain patients may exhibit circumstances where RVpacing may not be necessary.

To this end, LV lead design and device algorithms have improved patientoutcomes during cardiac resynchronization therapy (CPT). LV only pacinghas been shown to be as efficient at conventional biventricular pacingin patients with wide QRS duration, intact atrioventricular (AV)conduction and left bundle branch block (LBBB).

However, LV only pacing can result in ventricle oversensing, ordouble-counting, of ventricle events in the right ventricle lead (RV),i.e. intrinsic or LV pacing wave front. Additionally, LV only pacing canalso lead to ventricle oversensing if the ventricle refractory window istoo short.

BRIEF SUMMARY

In accordance with embodiments herein, a system is provided forcontrolling a left univentricular (LUV) pacing therapy using animplantable medical device (IMD). The system includes electrodesconfigured to be located proximate to an atrial (A) site, a leftventricular (LV) site and a right ventricular (RV) site of the heart, asensing circuitry configured to define an atrial sensing channel and anRV sensing channel, and a memory to store program instructions. Thesystem also includes one or more processors configured to implement theprogram instructions to determine an atrial-ventricular (AV) conductioninterval (AR_(RV)) between the A site and a first RV sensed event at theRV site, determine an inter-ventricular (VV) conduction interval(R_(LV)-R_(RV)) between a paced event at the LV site and a second RVsensed event at the RV site, and set a ventricular refractory period(VRP) based on at least one of the AV conduction interval or the VVconduction interval and a predetermined offset. The one or moreprocessors are also configured to blank signals over the RV sensingchannel during the VRP, and manage the LUV pacing therapy based on thesignals sensed over the RV sensing channel outside of the VRP, whereinthe LUV pacing therapy lacks pacing in the RV.

Optionally, the LUV pacing therapy is not based on signals sensed in theLV. In another aspect, the one or more processors also deliver an Apaced event at the A site, obtain cardiac activity (CA) signals over theRV sensing channel, and identify the first RV sensed event from the CAsignals obtained over the RV sensing channel, the AV conduction intervaldetermined based on a time between the A paced event and the first RVsensed event. In another aspect, the one or more processors also deliveran LV paced event at the LV site, obtain cardiac activity (CA) signalsover the RV sensing channel, and identify the second RV sensed eventfrom the CA signals obtained over the RV sensing channel, the VVconduction interval determined based on the time between the LV pacedevent and the second RV sensed event.

Optionally, the sensing circuitry does not obtain signals at the LVsite. In one aspect the one or more processors identify a longer one ofthe AV conduction interval and the VV conduction interval, the VRP setbased on the longer one of the AV and VV conduction intervals. Inanother aspect, the VRP defines a blanking interval during whichsignals, that occur over the RV sensing channel, are ignored.

In one or more embodiments, a computer implemented method forcontrolling a left univentricular (LUV) pacing therapy using animplantable medical device (IMD) is provided. The method includesdetermining an atrial-ventricular (AV) conduction interval (AR_(RV))between an atrial (A) site and a first right ventricular (RV) sensedevent at a RV site, determining an inter-ventricular (VV) conductioninterval (R_(LV)-R_(RV)) between a paced event at a left ventricular(LV) site and a second RV sensed event at the RV site, and setting aventricular refractory period (VRP) based on at least one of the AVconduction interval or the VV conduction interval and a predeterminedoffset. The method may also include blanking signals over a RV sensingchannel during the VRP, and managing the LUV pacing therapy based on thesignals sensed over the RV sensing channel outside of the VRP, whereinthe LUV pacing therapy lacks pacing in the RV.

Optionally, the LUV pacing therapy is not based on signals sensed in theLV. In another aspect the method also includes delivering an A pacedevent at the A site, obtaining cardiac activity (CA) signals over the RVsensing channel, and identifying the first RV sensed event from the CAsignals obtained over the RV sensing channel, the AV conduction intervaldetermined based on a time between the A paced event and the first RVsensed event. In another aspect, the method also includes delivering anLV paced event at the LV site, obtaining cardiac activity (CA) signalsover the RV sensing channel and identifying the second RV sensed eventfrom the CA signals obtained over the RV sensing channel, the VVconduction interval determined based on the time between the LV pacedevent and the second RV sensed event.

Optionally, the sensing circuitry does not obtain signals at the LVsite. In one aspect, the method also includes identifying a longer oneof the AV conduction interval and the VV conduction interval, the VRPset based on the longer one of the AV and VV conduction intervals. Inanother aspect, the VRP defines a blanking interval during whichsignals, that occur over the RV sensing channel, are ignored.

In one or more embodiments, a system for controlling a leftuniventricular (LUV) pacing therapy using an implantable medical device(IMD) is provided. The system includes electrodes configured to belocated proximate to an atrial (A) site, a left ventricular (LV) siteand a right ventricular (RV) site of the heart; sensing circuitryconfigured to define an atrial sensing channel and an RV sensingchannel, and memory to store program instructions. The system alsoincludes one or more processors configured to implement the programinstructions to determine an atrial-ventricular (AV) conduction interval(AR_(RV)) between the A site and a first RV sensed event at the RV site,determine an inter-ventricular (VV) conduction interval (R_(LV)-R_(RV))between a paced event at the LV site and a second RV sensed event at theRV site, and set a ventricular refractory period (VRP) based on at leastone of the AV conduction interval or the VV conduction interval and apredetermined offset. The one or more processors are also configured toblank signals over the RV sensing channel during the VRP, manage the LUVpacing therapy based on the signals sensed over the RV sensing channeloutside of the VRP, wherein the LUV pacing therapy lacks pacing in theRV, and identify a longer one of the AV conduction interval and the VVconduction interval, the VRP set based on the longer one of the AV andVV conduction interval. The VRP defines a blanking interval during whichsignals, that occur over the RV sensing channel, are ignored.

Optionally, the LUV pacing therapy is not based on signals sensed in theLV. In one aspect the one or more processors also deliver an A pacedevent at the A site, obtain cardiac activity (CA) signals over the RVsensing channel, and identify the first RV sensed event from the CAsignals obtained over the RV sensing channel, the AV conduction intervaldetermined based on a time between the A paced event and the first RVsensed event. In one aspect, the one or more processors also deliver anLV paced event at the LV site, obtain cardiac activity (CA) signals overthe RV sensing channel and identifying the second RV sensed event fromthe CA signals obtained over the RV sensing channel, the VV conductioninterval determined based on the time between the LV paced event and thesecond RV sensed event. In another aspect, the sensing circuitry doesnot obtain signals at the LV site. In one example, the one or moreprocessors also determine the first RV sensed event is not a postventricular contraction (PVC); and counting the first RV sensed event.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary IMD formed in accordance withembodiments herein.

FIG. 2 shows a block diagram of an exemplary IMD that is implanted intothe patient as part of the implantable cardiac system in accordance withembodiments herein.

FIG. 3 illustrates a flow block diagram of a method for controlling leftuniventricular (LUV) pacing therapy using an IMD in accordance withembodiments herein.

FIG. 4 illustrates a flow block diagram of a method of automaticallyupdating a ventricular refractory period (VRP) in accordance withembodiments herein.

FIG. 5 illustrates an anatomical diagram of a heart in accordance withembodiments herein.

FIG. 6 illustrates a waveform sensed by an IMD in accordance withembodiments herein.

DETAILED DESCRIPTION

It will be readily understood that the components of the embodiments asgenerally described and illustrated in the figures herein, may bearranged and designed in a wide variety of different configurations inaddition to the described example embodiments. Thus, the following moredetailed description of the example embodiments, as represented in thefigures, is not intended to limit the scope of the embodiments, asclaimed, but is merely representative of example embodiments.

Reference throughout this specification to “one embodiment” or “anembodiment” (or the like) means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment. Thus, appearances of the phrases “in oneembodiment” or “in an embodiment” or the like in various placesthroughout this specification are not necessarily all referring to thesame embodiment.

Furthermore, the described features, structures, or characteristics maybe combined in any suitable manner in one or more embodiments. In thefollowing description, numerous specific details are provided to give athorough understanding of embodiments. One skilled in the relevant artwill recognize, however, that the various embodiments can be practicedwithout one or more of the specific details, or with other methods,components, materials, etc. In other instances, well-known structures,materials, or operations are not shown or described in detail to avoidobfuscation. The following description is intended only by way ofexample, and simply illustrates certain example embodiments.

The system and methods described herein are provided to avoid RV leadoversensing by adjusting the ventricular refractory period based on theright atrial (RA) and LV to RV sensed delays. In particular, the delayfrom LV paced to the RV sensed are measured (LVp-RVs) at the shortestpossible paced/sensed AV delay to ensure sensing in the RV is due to LVpacing wave front, where the measurement is LVp-RVs. The delay from theRA paced and RA sensed is measured to the RV with no LV pacing, wherethe measurement is RAp/RAs-RVs. The ventricle refractory period (VRP) isprogrammed to Xms longer than the largest measurement betweenRAp/RAs-RVs and LVp-RVs. A RVs counter is initialized to 0. The systemthen continuously records if a ventricle sensed event is detected justoutside of the VRP. If an event is sensed, first it is verified if theorigin is a premature ventricular contraction (PVC). If so, monitoringcontinues. If not, then a RVs counter is increased by 1 (RVs=RVs+1).When the RVs counter reaches a threshold, or maximum of sensed beats,the delays (LVp-RVs and RAp/RAs-RVs) are measured again and the VRP isupdated.

The terms “beat”, and “event” are used interchangeably and refer to bothnormal and/or abnormal events.

The terms “cardiac activity signal”, “cardiac activity signals”, “CAsignal” and “CA signals” (collectively “CA signals”) are usedinterchangeably throughout to refer to an analog or digital electricalsignal recorded by two or more electrodes positioned subcutaneous orcutaneous, where the electrical signals are indicative of cardiacelectrical activity. The cardiac activity may be normal/healthy orabnormal/arrhythmic. Non-limiting examples of CA signals include ECGsignals obtained by cutaneous electrodes, and EGM signals obtained bysubcutaneous electrodes.

The term “delay” shall refer to a parameter programmed or set inconnection with the operation of the IMD. For example, an IMD may have aprogrammed AV delay, post ventricular atrial refractory period (PVARP)delay, and the like.

The term “ignored” shall mean to intentionally disregard. In examples,intentionally disregarding a sensed event can be accomplished by notmonitoring an event, not sensing an event, not communicating a sensedevent, not using information associated with a sensed event in ananalysis, algorithm, function, equation, etc., eliminating or not usinganalysis made with a sensed event, or the like. In each example, theevent sensed is considered a blanked event sensed, or ignored throughblanking or a blanking signal.

The term “IMD” shall mean an implantable medical device. Embodiments maybe implemented in connection with one or more implantable medicaldevices (IMDs). Non-limiting examples of IMDs include one or more ofneurostimulator devices, implantable leadless monitoring and/or therapydevices, and/or alternative implantable medical devices. For example,the IMD may represent a cardiac monitoring device, pacemaker,cardioverter, cardiac rhythm management device, defibrillator,neurostimulator, leadless monitoring device, leadless pacemaker, and thelike. The IMD may measure electrical and/or mechanical information. Forexample, the IMD may include one or more structural and/or functionalaspects of the device(s) described in U.S. Pat. No. 9,333,351, entitled“NEUROSTIMULATION METHOD AND SYSTEM TO TREAT APNEA” issued May 10, 2016and U.S. Pat. No. 9,044,610, entitled “SYSTEM AND METHODS FOR PROVIDINGA DISTRIBUTED VIRTUAL STIMULATION CATHODE FOR USE WITH AN IMPLANTABLENEUROSTIMULATION SYSTEM” issued Jun. 2, 2015, which are herebyincorporated by reference. The IMD may monitor transthoracic impedance,such as implemented by the CorVue algorithm offered by St. Jude Medical.Additionally or alternatively, the IMD may include one or morestructural and/or functional aspects of the device(s) described in U.S.Pat. No. 9,216,285, entitled “LEADLESS IMPLANTABLE MEDICAL DEVICE HAVINGREMOVABLE AND FIXED COMPONENTS” issued Dec. 22, 2015 and U.S. Pat. No.8,831,747, entitled “LEADLESS NEUROSTIMULATION DEVICE AND METHODINCLUDING THE SAME” issued Sep. 9, 2014, which are hereby incorporatedby reference. Additionally or alternatively, the IMD may include one ormore structural and/or functional aspects of the device(s) described inU.S. Pat. No. 8,391,980, entitled “METHOD AND SYSTEM FOR IDENTIFYING APOTENTIAL LEAD FAILURE IN AN IMPLANTABLE MEDICAL DEVICE” issued Mar. 5,2013 and U.S. Pat. No. 9,232,485, entitled “SYSTEM AND METHOD FORSELECTIVELY COMMUNICATING WITH AN IMPLANTABLE MEDICAL DEVICE” issuedJan. 5, 2016, which are hereby incorporated by reference. Additionallyor alternatively, the IMD may be a subcutaneous IMD that includes one ormore structural and/or functional aspects of the device(s) described inU.S. application Ser. No. 15/973,195, entitled “SUBCUTANEOUSIMPLANTATION MEDICAL DEVICE WITH MULTIPLE PARASTERNAL-ANTERIORELECTRODES” filed May 7, 2018; U.S. application Ser. No. 15/973,219,entitled “IMPLANTABLE MEDICAL SYSTEMS AND METHODS INCLUDING PULSEGENERATORS AND LEADS” filed May 7, 2018; U.S. application Ser. No.15/973,249, entitled “SINGLE SITE IMPLANTATION METHODS FOR MEDICALDEVICES HAVING MULTIPLE LEADS”, filed May 7, 2018, U.S. application Ser.No. 15/672,178, entitled “METHOD AND DEVICE FOR CONTROLLING LEFTVENTRICULAR PACING THERAPY”, filed Aug. 8, 2017, which are herebyincorporated by reference in their entireties. Further, one or morecombinations of IMDs may be utilized from the above incorporated patentsand applications in accordance with embodiments herein. Embodiments maybe implemented in connection with one or more subcutaneous implantablemedical devices (S-IMDs). For example, the S-IMD may include one or morestructural and/or functional aspects of the device(s) described in U.S.application Ser. No. 15/973,219, entitled “IMPLANTABLE MEDICAL SYSTEMSAND METHODS INCLUDING PULSE GENERATORS AND LEADS”, filed May 7, 2018;U.S. application Ser. No. 15/973,195, entitled “SUBCUTANEOUSIMPLANTATION MEDICAL DEVICE WITH MULTIPLE PARASTERNAL-ANTERIORELECTRODES”, filed May 7, 2018; which are hereby incorporated byreference in their entireties. The IMD may represent a passive devicethat utilizes an external power source, and entirely mechanical planwill device, and/or an active device that includes an internal powersource. The IMD may deliver some type of therapy/treatment, providemechanical circulatory support, and/or merely monitor one or morephysiologic characteristics of interest (e.g., PAP, CA signals,impedance, heart sounds).

The term “interval” shall refer to an intrinsic characteristic of ananatomy. For example, a heart exhibits an intrinsic AV conductioninterval, VV conduction interval and the like.

The terms “left univentricular pacing”, “LUV pacing” and “leftventricular only pacing” are used interchangeably to refer to pacingtherapies that deliver pacing stimulation at one or more leftventricular (LV) sites and do not deliver any pacing stimulation to anyright ventricular (RV) sites. The terms “left univentricular pacing”,“LUV” and “left ventricular only pacing” include therapies that deliveratrial pacing, but do not include biventricular pacing therapies.

The term “non-pacing/sensing electrode” refers to an electrode that iscontrolled and utilized only for sensing operations. Thenon-pacing-sensing electrode may be on a lead coupled to a lead-basedimplantable medical device and/or external programmer to perform sensingof cardiac signals at the corresponding site, and is not controlled orutilized to deliver pacing pulses. The non-pacing-sensing electrode maybe on a leadless implantable medical device that uses the electrode toperform sensing of cardiac signals at the corresponding site, and doesnot use the electrode to deliver pacing pulses.

The term “obtains” and “obtaining”, as used in connection with data,signals, information and the like, include at least one of i) accessingmemory of an external device or remote server where the data, signals,information, etc. are stored, ii) receiving the data, signals,information, etc. over a wireless communications link between the ICMand a local external device, and/or iii) receiving the data, signals,information, etc. at a remote server over a network connection. Theobtaining operation, when from the perspective of an ICM, may includesensing new signals in real time, and/or accessing memory to read storeddata, signals, information, etc. from memory within the ICM. Theobtaining operation, when from the perspective of a local externaldevice, includes receiving the data, signals, information, etc. at atransceiver of the local external device where the data, signals,information, etc. are communicated from an IMD and/or a remote server.The obtaining operation may be from the perspective of a remote server,such as when receiving the data, signals, information, etc. at a networkinterface from a local external device and/or directly from an IMD. Theremote server may also obtain the data, signals, information, etc. fromlocal memory and/or from other memory, such as within a cloud storageenvironment and/or from the memory of a workstation or clinicianexternal programmer.

The term “pacing/sensing electrode” refers to an electrode that iscontrolled and utilized by an implantable medical device and/or externalprogrammer to perform both delivery of pacing pulses at a site andsensing of cardiac signals at the same site.

The terms “processor,” “a processor”, “one or more processors” and “theprocessor” shall mean one or more processors. The one or more processorsmay be implemented by one, or by a combination of more than oneimplantable medical device, a wearable device, a local device, a remotedevice, a server computing device, a network of server computing devicesand the like. The one or more processors may be implemented at a commonlocation or at distributed locations. The one or more processors mayimplement the various operations described herein in a serial orparallel manner, in a shared-resource configuration and the like.

The phrase “wherein the LUV pacing therapy is not based on signalssensed in the LV” shall mean that left univentricular pacing is providedbased on signals sensed in an area of the heart other than the LV. Thesensing instead may occur in the A, and/or RV, but no the LV.

FIG. 1 illustrates an exemplary IMD 100 formed in accordance withembodiments herein. The IMD 100 is shown in electrical communicationwith a heart 112 by way of a right atrial lead 120 having an atrial tipelectrode 122 and an atrial ring electrode 123 implanted in the atrialappendage. The IMD 100 is also in electrical communication with theheart by way of a right ventricular lead 130 having, in this embodiment,a ventricular tip electrode 132, a right ventricular ring electrode 134,a right ventricular (RV) coil electrode 136, and a superior vena cava(SVC) coil electrode 138. Typically, the right ventricular lead 130 istransvenously inserted into the heart so as to place the RV coilelectrode 136 in the right ventricular apex, and the SVC coil electrode138 in the superior vena cava. Accordingly, the right ventricular leadis capable of receiving cardiac signals, and delivering stimulation inthe form of pacing and shock therapy to the right ventricle.

To sense left atrial and ventricular cardiac signals and to provide leftchamber pacing therapy, IMD 100 is coupled to a multi-pole LV lead 124designed for placement in the “CS region” via the CS OS for positioninga distal electrode adjacent to the left ventricle and/or additionalelectrode(s) adjacent to the left atrium. As used herein, the phrase “CSregion” refers to the venous vasculature of the left ventricle,including any portion of the CS, great cardiac vein, left marginal vein,left posterior ventricular vein, middle cardiac vein, and/or smallcardiac vein or any other cardiac vein accessible by the CS.Accordingly, an exemplary LV lead 124 is designed to receive atrial andventricular cardiac signals and to deliver left ventricular pacingtherapy using a set of four left ventricular electrodes 126 ₁, 126 ₂,126 ₃, and 126 ₄ (thereby providing a quadripole lead), left atrialpacing therapy using at least a left atrial ring electrode 127, andshocking therapy using at least a left atrial coil electrode 128implanted on or near the left atrium. In other examples, more or fewerLV electrodes are provided. Although only three leads are shown, itshould be understood that additional leads (with one or more pacing,sensing and/or shocking electrodes) might be used and/or additionalelectrodes might be provided on the leads already shown, such asadditional electrodes on the RV lead. In this manner, electrodes areconfigured to be located proximate to an atrial (A) site, leftventricular (LV) site and right ventricular (RV) site of the heart

FIG. 2 shows a block diagram of an exemplary IMD 100 that is implantedinto the patient as part of the implantable cardiac system. The IMD 100may be implemented as a full-function biventricular pacemaker, equippedwith both atrial and ventricular sensing, and pacing circuitry for fourchamber sensing and stimulation therapy (including both pacing and shocktreatment). Optionally, the IMD 100 may provide full-function cardiacresynchronization therapy. Alternatively, the IMD 100 may be implementedwith a reduced set of functions and components. For instance, the IMDmay be implemented without ventricular sensing and pacing. As describedherein, the IMD 100 is configured to provide LUV pacing therapy withoutpacing the RV.

The IMD 100 has a housing 201 to hold the electronic/computingcomponents. The housing 201 (which is often referred to as the “can”,“case”, “encasing”, or “case electrode”) may be programmably selected toact as the return electrode for certain stimulus modes. Housing 201further includes a connector (not shown) with a plurality of terminals,a portion of which are designated as terminals 202, 204, 206, 208, and210. The terminals may be connected to electrodes that are located invarious locations within and about the heart. For example, the terminalsmay include: a terminal 202 to be coupled to an first electrode (e.g., atip electrode) located in a first chamber; a terminal 204 to be coupledto a second electrode (e.g., tip electrode) located in a second chamber;a terminal 206 to be coupled to an electrode (e.g., ring) located in thefirst chamber; a terminal 208 to be coupled to an electrode located(e.g., ring electrode) in the second chamber; and a terminal 210 to becoupled to an electrode (e.g., coil) located in the SVC. The type andlocation of each electrode may vary. For example, the electrodes mayinclude various combinations of ring, tip, coil and shocking electrodesand the like. It is understood that more or fewer terminals may beutilized. With reference to FIG. 1, the housing 201 includes at least anumber of terminals corresponding to the number of electrodes providedon leads 120, 124 and 130. For example, terminals are provided toconnect to the LV electrodes 126 ₁-126 ₄.

The IMD 100 includes a programmable microcontroller 220 that controlsvarious operations of the IMD 100, including cardiac monitoring andstimulation therapy. Microcontroller 220 includes a microprocessor (orequivalent control circuitry), RAM and/or ROM memory, logic and timingcircuitry, state machine circuitry, and I/O circuitry.

The IMD 100 further includes one or more pulse generators 222 thatgenerates stimulation pulses for delivery by one or more electrodescoupled thereto. The pulse generator 222 is controlled by themicrocontroller 220 via control signal 224. The pulse generator 222 iscoupled to the select electrode(s) via an electrode configuration switch226, which includes multiple switches for connecting the desiredelectrodes to the appropriate I/O circuits, thereby facilitatingelectrode programmability. The switch 226 is controlled by a controlsignal 228 from the microcontroller 220.

In the example of FIG. 2, a single pulse generator 222 is illustrated.Optionally, the IMD 100 may include multiple pulse generators, similarto pulse generator 222, where each pulse generator is coupled to one ormore electrodes and controlled by the microcontroller 220 to deliverselect stimulus pulse(s) to the corresponding one or more electrodes.

The IMD 100 includes sensing circuitry 230 selectively coupled to one ormore electrodes that perform sensing operations, through the switch 226to detect the presence of cardiac activity in the right chambers of theheart. The sensing circuitry 230 may include dedicated sense amplifiers,multiplexed amplifiers, or shared amplifiers. It may further employ oneor more low power, precision amplifiers with programmable gain and/orautomatic gain control, bandpass filtering, and threshold detectioncircuit to selectively sense the cardiac signal of interest. Theautomatic gain control enables the IMD 100 to sense low amplitude signalcharacteristics of atrial fibrillation. The sensing circuitry 230 isconfigured to define an atrial sensing channel and an RV sensing channelwhere signals are received from each individual channel by the sensingcircuitry 230. Switch 226 determines the sensing polarity of the cardiacsignal by selectively closing the appropriate switches. In this way, theclinician may program the sensing polarity independent of thestimulation polarity.

The output of the sensing circuitry 230 is connected to themicrocontroller 220 which, in turn, triggers or inhibits the pulsegenerator 222 in response to the absence or presence of cardiacactivity. The sensing circuitry 230 receives a control signal 231 fromthe microcontroller 220 for purposes of controlling the gain, threshold,polarization charge removal circuitry (not shown), and the timing of anyblocking circuitry (not shown) coupled to the inputs of the sensingcircuitry.

In the example of FIG. 2, sensing circuitry 230 with a single sensingcircuit is illustrated. Optionally, the IMD 100 may include multiplesensing circuits, similar to sensing circuitry 230, where each sensingcircuit is coupled to one or more electrodes and controlled by themicrocontroller 220 to sense electrical activity detected at thecorresponding one or more electrodes. The sensing circuitry 230 mayoperate in a unipolar sensing configuration or in a bipolar sensingconfiguration.

Microcontroller 220 is illustrated to include timing control circuitry232 to control the timing of the stimulation pulses (e.g., pacing rate,atrio-ventricular conduction (AR_(RV)) delay or interval, ventricular(V-V) conduction (R_(LV)-R_(RV)) delay or interval, etc.). In connectionwith embodiments herein, the timing control circuitry 232 is used tomanage the timing of refractory periods, and blanking intervalsassociated with the refractory periods. Microcontroller 220 also has anarrhythmia detector 234 for detecting arrhythmia conditions and amorphology detector 236 to review and analyze one or more features ofthe morphology of cardiac signals.

The microcontroller 220 includes LUV therapy control circuitry 233 toimplement the processes described herein for controlling an LVuniventricular pacing therapy. The LUV therapy control circuitry 233determines the AR_(RV) (AV) conduction interval and R_(LV)-R_(RV) (VV)conduction interval, and sets a ventricular refractory period (VRP)based on a comparison of the AV conduction interval and VV conductioninterval. The VRP includes an offset, and the LUV therapy controlcircuitry 233 blanks signals over an RV sensing channel during thedetermined VRP to manage the LUV pacing therapy.

The LUV therapy control circuitry 233 obtains CA signals over the RVsensing channel of the sensing circuitry 230, the AV conduction intervaldetermined based on a time between an atrial paced event and a first RVsensed event. The LUV therapy control circuitry 233 also deliverers anLV paced event at a LV site to obtain CA signals over the RV sensingchannel of the sensing circuitry 230 and identify the time between theLV paced event and the RV sensed event to provide the VV conductioninterval. The LUV therapy control circuitry 233, optionally, does notobtain signals at the LV site. The LUV therapy control circuitry 233also identifies a longer one of the AV conduction interval and the VVconduction interval and sets the VRP based on the longer of the AV andVV conduction intervals.

The IMD 100 is further equipped with a communication modem(modulator/demodulator) 240 to enable wireless communication with otherdevices, implanted devices, and/or external devices. In oneimplementation, the communication modem 240 may use high frequencymodulation of a signal transmitted between a pair of electrodes. As oneexample, the signals may be transmitted in a high frequency range ofapproximately 10-80 kHz, as such signals travel through the body tissueand fluids without stimulating the heart or being felt by the patient.

The communication modem 240 may be implemented in hardware as part ofthe microcontroller 220, or as software/firmware instructions programmedinto and executed by the microcontroller 220. Alternatively, the modem240 may reside separately from the microcontroller as a standalonecomponent.

The IMD 100 further includes an analog-to-digital (ND) data acquisitionsystem (DAS) 250 coupled to one or more electrodes via the switch 226 tosample cardiac signals across any pair of desired electrodes. The dataacquisition system 250 is configured to acquire intracardiac electrogramsignals, convert the raw analog data into digital data, and store thedigital data for later processing and/or telemetric transmission to anexternal device 254 (e.g., a programmer, local transceiver, or adiagnostic system analyzer). The data acquisition system 250 iscontrolled by a control signal 256 from the microcontroller 220.

The microcontroller 220 is coupled to a memory 260 by a suitabledata/address bus 262. The programmable operating parameters used by themicrocontroller 220 are stored in memory 260 and used to customize theoperation of the IMD 100 to suit the needs of a particular patient. Suchoperating parameters define, for example, pacing pulse amplitude, pulseduration, electrode polarity, rate, sensitivity, automatic features,arrhythmia detection criteria, and the amplitude, wave shape and vectorof each shocking pulse to be delivered to the patient's heart withineach respective tier of therapy.

The memory 260 is configured to store the VRP set by the LUV therapycontrol circuitry 233 based on the AV conduction interval and VVconduction interval. In addition, the sensing circuitry 230 continuesdetermining AV conduction intervals and VV conduction intervals todetermine when a RV event is not a PVC. In each instance, themicrocontroller adds a count to a stored false PVC count. Once the falsePVC count reaches and/or exceeds a threshold amount, such as threecounts, a LV paced event is delivered to redetermine the VRP. In oneexample, the threshold amount may be determined based on a timedependent basis such that the threshold amount must be reached during adetermined period. In an example, the determined period could be a day,such that if three false PVCs occur in a twenty-four hour period, theVRP is redetermined.

A battery 272 provides operating power to all of the components in theIMD 100. The battery 272 is capable of operating at low current drainsfor long periods of time, and is capable of providing high-currentpulses (for capacitor charging) when the patient requires a shock pulse(e.g., in excess of 2 A, at voltages above 2 V, for periods of 10seconds or more). The battery 272 also desirably has a predictabledischarge characteristic so that elective replacement time can bedetected.

The IMD 100 can be operated as an implantable cardioverter/defibrillator(ICD) device, which detects the occurrence of an arrhythmia andautomatically applies an appropriate electrical shock therapy to theheart aimed at terminating the detected arrhythmia. To this end, themicrocontroller 220 further controls a shocking circuit 280 by way of acontrol signal 282. The shocking circuit 280 generates shocking pulsesof low (e.g., up to 0.5 joules), moderate (e.g., 0.5-10 joules), or highenergy (e.g., 11 to 40 joules), as controlled by the microcontroller220. Such shocking pulses are applied to the patient's heart 112 throughshocking electrodes. It is noted that the shock therapy circuitry isoptional and may not be implemented in the IMD, as the various slavepacing units described below will typically not be configured to deliverhigh voltage shock pulses. On the other hand, it should be recognizedthat the slave pacing unit can be used within a system that includesbackup shock capabilities, and hence such shock therapy circuitry may beincluded in the IMD.

FIG. 3 illustrates a method for controlling left univentricular (LUV)pacing therapy using an implantable medical device (IMD). In oneembodiment, the IMD of FIGS. 1 and 2 accomplishes the method. In anotherembodiment, the method is accomplished by an IMD that lacks, or does notinclude, RV pacing, and is providing only LV pacing.

At 302, an IMD delivers an atrial (A) paced event at an A site. The Asite may include any location within the right atrial. Alternatively,the IMD senses an A event. To this end, any of the step 304-308 may beapplied to an IMD sensing an A event. At 304, one or more processorsobtain electrical cardiac activity (CA) signals over a right ventricle(RV) sensing channel. In one embodiment, the RV sensing channel isdefined by sensing circuitry that monitors electrical activity of theheart. In one example, the sensing circuitry is the sensing circuitrydescribed in relation to FIG. 2. The RV sensing channel extends along anRV sensing vector through a desired portion of the right ventricle. Inthis manner, the paced event at the A site is sensed at a RV site.

At 306, the one or more processors analyze the cardiac activity signalsto identify a RV sensed event that occurred in response to the A pacedevent. For the method 300, the RV sensed event is a first RV sensedevent that is associated with the IMD pacing, whereas concurrently, anLV paced event is also delivered, providing a second RV sensed event(e.g. 310-316). Optionally, the RV sensed event identified from the LVpaced event may be considered a first RV sensed event, while the RVsensed event identified from the delivered A paced event may beconsidered the second RV sensed event. In one example, the delay fromthe RA paced event and RV sensed event (AV delay) is measured with no LVpacing. In one example, the RA paced event is approximately 10 bpmhigher than the intrinsic heart rate. In one example, the AV delay isapproximately 50 ms while the sensed AV delay is approximately 25 ms.

At 308, the one or more processors determine an atrio-ventricle (AV)conduction interval (AR_(RV)) between the A paced event and the RVsensed event RAp/RAs-RVs. Additionally or alternatively, the operationat 306 may be implemented based on an intrinsic atrial event. Forexample, the one or more processors may sense an atrial intrinsic eventover the atrial sensing channel and record a timestamp at which theatrial event occurred. Thereafter, the one or more processors analyzethe CA signals sensed over the RV sensing channel for a correspondingsubsequent RV sensed event.

Subsequent to the operations at 302 to 308, the one or more processorsmanage the operations at 310 to 316. For example, the operations at 302to 308 may be performed during one beat and the operations at 310 to 316may be performed during the next (or a later) beat. Optionally, theoperations at 302 to 308 maybe repeated for a first group of beats todetermine the AV_(RV) based on an ensemble of beats. Thereafter, theoperations at 310 to 316 maybe repeated for a second group of beats todetermine the VV conduction internal R_(LV)-R_(RV) based on an ensembleof beats.

At 310, the one or more processors deliver a left ventricle (LV) pacedevent at one or more LV sites. At 312, the one or more processors obtainCA signals over the RV sensing channel as described above in relation to304.

At 314, the one or more processors identify the second RV sensed eventfrom the CA signals in connection with the LV paced event. The sensingcircuitry does not obtain signals at the LV site, and only signals fromthe RV sensing channel are utilized. Also, as indicated above, the RVsensed event may be considered the first RV sensed event or second RVsensed event. The delay from LV paced event to the RV sensed event aremeasured (LVp-RVs) at the shortest possible paced/sensed AV delay toensure sensing in the RV is due to the LV pacing wave front.

At 316, the one or more processors determine the inter-ventricular (VV)conduction interval (R_(LV)-R_(RV)). Additionally or alternatively, theoperation at 306 may be implemented based on an intrinsic ventricleevent. For example, the one or more processors may sense a ventricleintrinsic event over the ventricle sensing channel and record atimestamp at which the ventricle event occurred. Thereafter, the one ormore processors analyze the CA signals sensed over the RV sensingchannel for a corresponding subsequent RV sensed event.

At 318, the one or more processors determine whether the AV conductioninterval is longer than the VV conduction interval. In one embodiment,the one or more processors compare lengths of the VV conduction intervaland AV conduction interval to identify which is longer. If the AVconduction interval is longer, flow moves to 320. At 320, the one ormore processors add a predetermined offset to the determined AVconduction interval to set a ventricular refractory period (VRP). Thepredetermined offset is a determined amount of time to account for errorand/or randomness, and in one example may be between 10 ms to 50 ms. Inother embodiments, the predetermined offset is greater than 50 ms. Thepredetermined offset may be preprogrammed by a clinician orautomatically determined by the IMD. For example, the predeterminedoffset may be set by a clinician to a desired number milliseconds orpercentage of the VV or AV conduction interval. When the predeterminedoffset is determined automatically, the IMD may define the predeterminedoffset based on the function of the longer of the VV or AV conductionintervals. For example, the IMD may define the predetermined offset tobe 10% of the AV or VV conduction interval.

If the VV conduction interval is longer, flow moves to 322. At 322 theone or more processors add the predetermined offset to the determined VVconduction interval to set the VRP. Again, the predetermined offset maybe determined such that the predetermined offset is the same, whetherthe AV conduction interval is longer or the VV conduction interval islonger. At the time the VRP is set, the one or more processors mayoptionally start a counter set at zero to make determination regardingwhen to update or change the VRP as will be detailed in relation to FIG.4. In this manner, calibration may be provided for the system.

At 324, whether the AV conduction interval was longer, or the VVconduction interval, the one or more processors set a blanking intervalfor the RV sensing channel to blank signals over the RV sensing channelduring the VRP. The VRP corresponds to a blanking interval, which is aninterval of time during which signals that occur over the RV sensingchannel are ignored. In one example, the RV sensing channel stopscollecting CA signals during the blanking interval. Alternatively, theRV sensing channel receiving CA signals during the blanking interval,but does not pass the CA signals to the microprocessor during theblanking interval. In yet another embodiment, the RV sensing channelreceives signals, and communicates the signals to the one or moreprocessors; however, the one or more processors do not use such signalsin algorithms, functions, equations, etc. used to determine the presenceof an event.

In accordance with new and unique aspects herein, methods and systemsreduce ventricle oversensing when using LV only pacing by blanking thesignal during the VRP interval. Specifically, double-counting ofventricle events in the RV lead is reduced compared to systems not usingthis methodology. Additionally, the VRP is ensured to be more accurate,ensuring improved functionality of the system.

At 326, the IMD manages LUV pacing therapy using the VRP, and blankingthe signals during the VRP. In this manner, LV only pacing may beutilized without oversensing, which improves accuracy, improves therapyefficacy, and reduces power usage by the IMD. Specifically, LUV pacingtherapy is not based on signals sensed in the LV, or chamber wherepacing is occurring.

FIG. 4 illustrates a method for automatically updating a ventricularrefractory period (VRP) in accordance with embodiments herein. At 402,one or more processors of an implantable medical device implement LVonly pacing.

At 404, an LV paced event is delivered at one or more LV sites and theone or more processors obtain CA signals over the RV sensing channel.The one or more processors analyze the CA signals to identify an RVsensed event that occurred in response to the LV paced event. The one ormore processors determine a VV conduction interval between the LV pacedevent and the RV sensed event.

At 406, an atrial paced event is delivered at an A site and the one ormore processors obtain CA signals over the RV sensing channel. The oneor more processors analyze the CA signals to identify an RV sensed eventthat occurred in response to the A paced event. The one or moreprocessors determine an AV conduction interval between the atrial pacedevent on the RV sensed event. Additionally or alternatively, theoperation at 406 may be implemented based on intrinsic atrial event. Forexample, the one or more processors may sense an atrial intrinsic eventover the atrial sensing channel and record a timestamp at which theatrial event occurred. Thereafter, the one or more processors analyzethe CA signals sensed over the RV sensing channel for a correspondingsubsequent RV sensed event.

At 408, the one or more processors compare lengths of the VV conductioninterval and AV conduction interval to identify which is longer. The oneor more processors then utilize the longer of the VV conduction intervaland AV conduction interval, and add thereto a predetermined offset, toobtain a ventricular refractory period (VRP) to be used in connectionwith the RV sensing channel. As described in relation to the method ofFIG. 3, the predetermined offset may be preprogrammed by a clinician orautomatically determined by the IMD.

At 410, the one or more processors initiate or continue in LUV therapyutilizing the new VRP to define a blanking interval during which signalsare ignored when sensed over the RV sensing channel. At 410, the one ormore processors determine whether an RV event is sensed over the RVsensing channel outside of the VRP. When no RV is sensed outside of theVRP, the process continues to monitor subsequent beats at 410. Once abeat is detected at 410 for which an RV event is sensed outside of theVRP, flow continues to 412.

At 412, the one or more processors apply a PVC detection process todetermine whether the RV event that was sensed is due to a postventricular contraction (PVC). When the RV event is deemed to be due toa PVC, flow returns to 410. When the RV event is determined to not bedue to a PVC, flow continues to 414. At 414, an RV counter isincremented. The RV counter maintains a count of the number of eventsthat are sensed outside of the VRP.

At 416, the one or more processors determine whether the RV counter hasexceeded a threshold. For example, the threshold may be set to three,five and the like. When the RV counter exceeds a threshold, flow returnsto 404. Alternatively, when the RV counter does not exceed thethreshold, flow returns to 410. In this manner, the system continuouslyrecords if a ventricle sensed event is detected just outside of the VRP.If an event is sensed, first it is verified if the origin is a PVC. Ifso, then system continues monitoring. If it is not a PVC, then the RVscounter is increased by 1 (RVs=RVs+1) so that the system may be updated,or continuously calibrated. In one example, after a determined amount oftime, the counter may decrease by one to attempt to ensure recalibrationonly occurs when changes have occurred, and not due to a bad signal, ortemporary monitoring malfunction.

FIG. 5 illustrates an example anatomical diagram of the heart 500 inconnection with determining VRP in accordance with embodiments herein.Specifically, the illustration shows leads 502, 504, 506 of an IMDutilized for cardiac resynchronization therapy. A first lead 502 is inthe right atrium (RA) 508, a second lead 504 is in the right ventricle(RV) 510, and the third lead 506 is in the left ventricle (LV) 512.Using this arrangement, RA to RV sensed (either atrial sensed [RAs] oratrial paced [RAp]) and LV paced (LVp) to RVs delays are provided. Usingthe arrangement, the paced event and sensed event are in differentchambers of the heart. The delay from LVp to the RVs is measured asLVp-RVs 514 at the minimum possible paced and sensed AV delay to ensuresensing in the RV 510 is due to the LV pacing wave front. The pacing mayoccur at any point P4, M3, M2, or D1 to the RV. In one example, theminimum possible AV delay is 50 ms while the minimum possible sensed AVdelay is 25 ms. Meanwhile, the delay from the RA paced and RA sensedmeasurements is measured to the RV with no LV pacing. The measurement isRAp/RAs-RVs 516.

FIG. 6 shows a set of waveforms 610 that include an atrial event (e.g.,A sense), a ventricle event (e.g. V sense), and a RV unipolar event (RVunipolar) where RV oversensing is provided such that blanking of asignal would be advantageous. In the example, only LV pacing is providedat 120 ms after A pacing, and the pacing wave front is being detected bythe RV sensing detector. Using a blanking period during the period theoversensing is occurring prevents misdiagnosis. In particular, becauseonly LV pacing is provided, such sensing cannot be as a result of RVpacing, and therefore can be blanked as a known over sense. Because theover sensed signal occurs at a time that sensing of LV is not expected,blanking does not have a negative effect.

CLOSING

It should be clearly understood that the various arrangements andprocesses broadly described and illustrated with respect to the Figures,and/or one or more individual components or elements of sucharrangements and/or one or more process operations associated of suchprocesses, can be employed independently from or together with one ormore other components, elements and/or process operations described andillustrated herein. Accordingly, while various arrangements andprocesses are broadly contemplated, described and illustrated herein, itshould be understood that they are provided merely in illustrative andnon-restrictive fashion, and furthermore can be regarded as but mereexamples of possible working environments in which one or morearrangements or processes may function or operate.

As will be appreciated by one skilled in the art, various aspects may beembodied as a system, method, or computer (device) program product.Accordingly, aspects may take the form of an entirely hardwareembodiment or an embodiment including hardware and software that may allgenerally be referred to herein as a “circuit,” “module” or “system.”Furthermore, aspects may take the form of a computer (device) programproduct embodied in one or more computer (device) readable storagemedium(s) having computer (device) readable program code embodiedthereon.

Any combination of one or more non-signal computer (device) readablemedium(s) may be utilized. The non-signal medium may be a storagemedium. A storage medium may be, for example, an electronic, magnetic,optical, electromagnetic, infrared, or semiconductor system, apparatus,or device, or any suitable combination of the foregoing. More specificexamples of a storage medium would include the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), a dynamicrandom access memory (DRAM), a read-only memory (ROM), an erasableprogrammable read-only memory (EPROM or Flash memory), a portablecompact disc read-only memory (CD-ROM), an optical storage device, amagnetic storage device, or any suitable combination of the foregoing.

Program code for carrying out operations may be written in anycombination of one or more programming languages. The program code mayexecute entirely on a single device, partly on a single device, as astand-alone software package, partly on single device and partly onanother device, or entirely on the other device. In some cases, thedevices may be connected through any type of network, including a localarea network (LAN) or a wide area network (WAN), or the connection maybe made through other devices (for example, through the Internet usingan Internet Service Provider) or through a hard wire connection, such asover a USB connection. For example, a server having a first processor, anetwork interface, and a storage device for storing code may store theprogram code for carrying out the operations and provide this codethrough its network interface via a network to a second device having asecond processor for execution of the code on the second device.

Aspects are described herein with reference to the figures, whichillustrate example methods, devices, and program products according tovarious example embodiments. The program instructions may be provided toa processor of a general purpose computer, special purpose computer, orother programmable data processing device or information handling deviceto produce a machine, such that the instructions, which execute via aprocessor of the device implement the functions/acts specified. Theprogram instructions may also be stored in a device readable medium thatcan direct a device to function in a particular manner, such that theinstructions stored in the device readable medium produce an article ofmanufacture including instructions which implement the function/actspecified. The program instructions may also be loaded onto a device tocause a series of operational steps to be performed on the device toproduce a device implemented process such that the instructions whichexecute on the device provide processes for implementing thefunctions/acts specified.

The units/modules/applications herein may include any processor-based ormicroprocessor-based system including systems using microcontrollers,reduced instruction set computers (RISC), application specificintegrated circuits (ASICs), field-programmable gate arrays (FPGAs),logic circuits, and any other circuit or processor capable of executingthe functions described herein. Additionally, or alternatively, themodules/controllers herein may represent circuit modules that may beimplemented as hardware with associated instructions (for example,software stored on a tangible and non-transitory computer readablestorage medium, such as a computer hard drive, ROM, RAM, or the like)that perform the operations described herein. The above examples areexemplary only, and are thus not intended to limit in any way thedefinition and/or meaning of the term “controller.” Theunits/modules/applications herein may execute a set of instructions thatare stored in one or more storage elements, in order to process data.The storage elements may also store data or other information as desiredor needed. The storage element may be in the form of an informationsource or a physical memory element within the modules/controllersherein. The set of instructions may include various commands thatinstruct the modules/applications herein to perform specific operationssuch as the methods and processes of the various embodiments of thesubject matter described herein. The set of instructions may be in theform of a software program. The software may be in various forms such assystem software or application software. Further, the software may be inthe form of a collection of separate programs or modules, a programmodule within a larger program or a portion of a program module. Thesoftware also may include modular programming in the form ofobject-oriented programming. The processing of input data by theprocessing machine may be in response to user commands, or in responseto results of previous processing, or in response to a request made byanother processing machine.

It is to be understood that the subject matter described herein is notlimited in its application to the details of construction and thearrangement of components set forth in the description herein orillustrated in the drawings hereof. The subject matter described hereinis capable of other embodiments and of being practiced or of beingcarried out in various ways. Also, it is to be understood that thephraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. The use of“including,” “comprising,” or “having” and variations thereof herein ismeant to encompass the items listed thereafter and equivalents thereofas well as additional items.

It is to be understood that the above description is intended to beillustrative, and not restrictive. For example, the above-describedembodiments (and/or aspects thereof) may be used in combination witheach other. In addition, many modifications may be made to adapt aparticular situation or material to the teachings herein withoutdeparting from its scope. While the dimensions, types of materials andcoatings described herein are intended to define various parameters,they are by no means limiting and are illustrative in nature. Many otherembodiments will be apparent to those of skill in the art upon reviewingthe above description. The scope of the embodiments should, therefore,be determined with reference to the appended claims, along with the fullscope of equivalents to which such claims are entitled. In the appendedclaims, the terms “including” and “in which” are used as theplain-English equivalents of the respective terms “comprising” and“wherein.” Moreover, in the following claims, the terms “first,”“second,” and “third,” etc. are used merely as labels, and are notintended to impose numerical requirements on their objects or order ofexecution on their acts.

What is claimed is:
 1. A system for controlling a left univentricular(LUV) pacing therapy using an implantable medical device (IMD), thesystem comprising: electrodes configured to be located proximate to anatrial (A) site, a left ventricular (LV) site and a right ventricular(RV) site of the heart; a sensing circuitry configured to define anatrial sensing channel and an RV sensing channel; memory to storeprogram instructions; one or more processors configured to implement theprogram instructions to: determine an atrial-ventricular (AV) conductioninterval (AR_(RV)) between the A site and a first RV sensed event at theRV site; determine an inter-ventricular (VV) conduction interval(R_(LV)-R_(RV)) between a paced event at the LV site and a second RVsensed event at the RV site; set a ventricular refractory period (VRP)based on at least one of the AV conduction interval or the VV conductioninterval and a predetermined offset; blank signals over the RV sensingchannel during the VRP; and manage the LUV pacing therapy based on thesignals sensed over the RV sensing channel outside of the VRP, whereinthe LUV pacing therapy lacks pacing in the RV.
 2. The system of claim 1,wherein the LUV pacing therapy is not based on signals sensed in the LV.3. The system of claim 1, the one or more processors are furtherconfigured to deliver an A paced event at the A site, obtain cardiacactivity (CA) signals over the RV sensing channel, and identify thefirst RV sensed event from the CA signals obtained over the RV sensingchannel, the AV conduction interval determined based on a time betweenthe A paced event and the first RV sensed event.
 4. The system of claim1, wherein the one or more processors are further configured to deliveran LV paced event at the LV site, obtain cardiac activity (CA) signalsover the RV sensing channel and identify the second RV sensed event fromthe CA signals obtained over the RV sensing channel, the VV conductioninterval determined based on the time between the LV paced event and thesecond RV sensed event.
 5. The system of claim 1, wherein the sensingcircuitry does not obtain signals at the LV site.
 6. The system of claim1, wherein the one or more processors are further configured to identifya longer one of the AV conduction interval and the VV conductioninterval, the VRP set based on the longer one of the AV and VVconduction intervals.
 7. The system of claim 1, wherein the VRP definesa blanking interval during which signals, that occur over the RV sensingchannel, are ignored.
 8. A computer implemented method for controlling aleft univentricular (LUV) pacing therapy using an implantable medicaldevice (IMD), the method comprising: determining an atrial-ventricular(AV) conduction interval (AR_(RV)) between an atrial (A) site and afirst right ventricular (RV) sensed event at a RV site; determining aninter-ventricular (VV) conduction interval (R_(LV)-R_(RV)) between apaced event at a left ventricular (LV) site and a second RV sensed eventat the RV site; setting a ventricular refractory period (VRP) based onat least one of the AV conduction interval or the VV conduction intervaland a predetermined offset; blanking signals over a RV sensing channelduring the VRP; and managing the LUV pacing therapy based on the signalssensed over the RV sensing channel outside of the VRP, wherein the LUVpacing therapy lacks pacing in the RV.
 9. The computer implementedmethod of claim 8, wherein the LUV pacing therapy is not based onsignals sensed in the LV.
 10. The computer implemented method of claim8, further comprising delivering an A paced event at the A site,obtaining cardiac activity (CA) signals over the RV sensing channel, andidentifying the first RV sensed event from the CA signals obtained overthe RV sensing channel, the AV conduction interval determined based on atime between the A paced event and the first RV sensed event.
 11. Thecomputer implemented method of claim 8, further comprising delivering anLV paced event at the LV site, obtaining cardiac activity (CA) signalsover the RV sensing channel and identifying the second RV sensed eventfrom the CA signals obtained over the RV sensing channel, the VVconduction interval determined based on the time between the LV pacedevent and the second RV sensed event.
 12. The computer implementedmethod of claim 8, wherein the sensing circuitry does not obtain signalsat the LV site.
 13. The computer implemented method of claim 8, furthercomprising identifying a longer one of the AV conduction interval andthe VV conduction interval, the VRP set based on the longer one of theAV and VV conduction intervals.
 14. The computer implemented method ofclaim 8, wherein the VRP defines a blanking interval during whichsignals, that occur over the RV sensing channel, are ignored.
 15. Asystem for controlling a left univentricular (LUV) pacing therapy usingan implantable medical device (IMD), the system comprising: electrodesconfigured to be located proximate to an atrial (A) site, a leftventricular (LV) site and a right ventricular (RV) site of the heart;sensing circuitry configured to define an atrial sensing channel and anRV sensing channel; memory to store program instructions; one or moreprocessors configured to implement the program instructions to:determine an atrial-ventricular (AV) conduction interval (AR_(RV))between the A site and a first RV sensed event at the RV site; determinean inter-ventricular (VV) conduction interval (R_(LV)-R_(RV)) between apaced event at the LV site and a second RV sensed event at the RV site;set a ventricular refractory period (VRP) based on at least one of theAV conduction interval or the VV conduction interval and a predeterminedoffset; blank signals over the RV sensing channel during the VRP; managethe LUV pacing therapy based on the signals sensed over the RV sensingchannel outside of the VRP, wherein the LUV pacing therapy lacks pacingin the RV; identify a longer one of the AV conduction interval and theVV conduction interval, the VRP set based on the longer one of the AVand VV conduction interval; and wherein the VRP defines a blankinginterval during which signals, that occur over the RV sensing channel,are ignored.
 16. The system of claim 15, wherein the LUV pacing therapyis not based on signals sensed in the LV.
 17. The system of claim 15,wherein the one or more processors are further configured to deliver anA paced event at the A site, obtain cardiac activity (CA) signals overthe RV sensing channel, and identify the first RV sensed event from theCA signals obtained over the RV sensing channel, the AV conductioninterval determined based on a time between the A paced event and thefirst RV sensed event.
 18. The system of claim 15, wherein the one ormore processors are further configured to deliver an LV paced event atthe LV site, obtain cardiac activity (CA) signals over the RV sensingchannel and identifying the second RV sensed event from the CA signalsobtained over the RV sensing channel, the VV conduction intervaldetermined based on the time between the LV paced event and the secondRV sensed event.
 19. The system of claim 15, wherein the sensingcircuitry does not obtain signals at the LV site.
 20. The system ofclaim 1, wherein the one or more processors are further configured todetermine the first RV sensed event is not a post ventricularcontraction (PVC); and counting the first RV sensed event.